(i) Field of the Invention
The present invention relates to an image reading apparatus for reading an image of the original by receiving light reflected from an original by an image pickup element.
(ii) Description of the Related Art
In a related art, there is known an image reading apparatus disclosed in JP-A-6-308627.
FIG. 2 shows the related art.
In FIG. 2, at an original 111 mounted on an original base plate 112 above an image reading apparatus 117, reflected image light is generated by light irradiated by a light source 113b provided at a first carriage 113, and the reflected light is reflected by reflecting members 113a at the first carriage, 114a and 114b provided at a second carriage and thereafter focused in the form of a line on CCD (Charge Couple Device) 116 which is an image pickup element via a focusing lens 115. The apparatus uses a reduction optical system.
Further, by moving the first carriage and the second carriage in a direction (the direction indicated by an arrow in the drawing, sub-scanning direction) orthogonal to a line direction (main scanning direction), an image of the original is successively scanned.
Here, an inverter 110 for supplying power to the light source is mounted at the first carriage.
Further, in recent years, as shown in FIG. 3, there is also proposed an apparatus in which a contact image sensor 121 having a length equal to or larger than an original width is mounted to the carriage 120 and an original image is read by equal magnification by scanning the original image. In the drawing, the same numerals as those of FIG. 2 designate members operated similarly. The apparatus uses an equal magnification optical system.
Further, the above-described two apparatus are generally the image reading apparatus enabling the original to be scanned by moving the original above a reading position without driving a scanning optical system by using an automatic original feeding apparatus.
Further, in many cases, when the apparatus main body is divided in two regions by a plane orthogonal to a main scanning direction of scanning means, it is general to arrange driving means (motor) of the scanning means to a side arranged with power supplying means to thereby shorten a length of a power line in order to prevent an increase in cost.
In recent years, reading time is rapidly faster at an image reading apparatus and in accordance therewith, in order to provide a necessary exposure quantity per unit time, it is indispensable to make brightness of scanning light higher.
Further, it is necessary to form a memory circuit or the like in a large scale for higher image quality and therefore, the signal processing circuit for outputting an image signal is also large-sized.
However, in making brightness of light source higher, the inverter is large-sized and the temperature of the inverter becomes high and therefore, when the inverter is mounted on the first carriage as in the related arts, the following problem is posed.
By an increase in weight of the scanning base, a large-sized formation of the driving means, an increase in the cost and an increase in power consumption are caused.
As shown in FIG. 4, according to a relationship between a position of the first carriage in a longitudinal direction and temperature of the light source, by influence of heat generation of the inverter, a temperature distribution of the light source in the longitudinal direction becomes extremely nonuniform, alight quantity in the longitudinal direction becomes nonuniform and therefore, partial fogging, lack of image or the like is brought about in an image reading signal.
According to the apparatus using the contact image sensor 121 as shown in FIG. 3, the contact image sensor 121 is mounted on a carriage 120 mounted with the inverter 110 and therefore, by influence of heat of the inverter 110, there is brought about image failure or malfunction of a CCD line sensor present at inside of the contact image sensor which is caused by exceeding guaranteed operation temperature.
Further, in case of mounting an inverter to an apparatus cabinet at an image reading apparatus using a reduction optical system, in order to thin the apparatus, it is general to mount the inverter more remote than an arrival position of the second carriage most remote from a home position to thereby prevent interference with the second carriage in moving and scanning operation. Therefore, the following problem is posed.
In the case of moving the original using a carrier belt by an automatic original feeding apparatus using the belt, the original moves when a first carriage of a scanning base is fixed at a vicinity of a center of an original base plate and a vicinity of an end side of the original base plate and therefore, when an inverter is arranged on a back side of an apparatus cabinet and forcedly cooled by cooling means (air blowing apparatus) 140, as shown in FIG. 6, hot wind passing through the inverter 110 flows in the longitudinal direction of a light source and therefore, a temperature distribution of the light source is made nonuniform and partial fogging, lack of image or the like is brought about in an image reading signal similar to the above-described.
When the inverter is arranged on the back side of the apparatus cabinet on the end side of the original base plate and forcedly cooled, hot air impinges also on CCD or a drive circuit thereof disposed downstream from the inverter as seen from the air blowing source. It causes also a problem of erroneous operation or malfunction of IC and the like.
In the case of arranging the inverter on the back side of the apparatus cabinet, when a board is arranged into the same size apparatus as that of the related art, the noise is liable to be picked up and a problem of image failure is liable to be brought about because connecting a control circuit board 161 for processing an image signal and controlling the apparatus and a communicating means 162 for outputting image data to other apparatus by a shortest distance as shown in FIG. 7 forces a signal line 163 to pass a vicinity of the inverter 110 constituting a source of noise by large-sized inverter.
When the inverter is arranged on the back side of the apparatus cabinet, as shown in FIG. 7 since an apparatus drive power source 164, a scanning means drive motor 166 and a driver circuit 165 that generate heat are concentrated on the back side of the apparatus cabinet, air warmed by heat from these members is blown to the inverter by cooling means 140, further, when a heat radiating member 110a directly connected to a heat radiating source of the inverter is connected to the apparatus cabinet, by heat conducted from these members to the apparatus cabinet, a time period taken until saturating temperature of the inverter is shortened and balancing temperature is elevated.
Here, as shown in FIG. 7, a cover 167 is provided with in order to prevent outside light from being incident on a CCD unit as much as possible and prevent emittance of noise from a CCD drive circuit 160, further, a cover 168 is provided with in order to prevent pickup of noise to the control circuit board 161 and emittance of noise.
Further, although JP-A-2001-119533 discloses an image reading apparatus arranged with an inverter 214 within a width of an optical system for illuminating and scanning an original, the problem by the heat of the inverter cannot be resolved.